Flexbox

The Flexbox Layout (Flexible Box) module (currently a W3C Last Call Working Draft) aims at providing a more efficient way to lay out, align and distribute space among items in a container, even when their size is unknown and/or dynamic (thus the word "flex").

The main idea behind the flex layout is to give the container the ability to alter its items' width/height (and order) to best fill the available space (mostly to accommodate to all kind of display devices and screen sizes). A flex container expands items to fill available free space, or shrinks them to prevent overflow.

Most importantly, the flexbox layout is direction-agnostic as opposed to the regular layouts (block which is vertically-based and inline which is horizontally-based). While those work well for pages, they lack flexibility (no pun intended) to support large or complex applications (especially when it comes to orientation changing, resizing, stretching, shrinking, etc.).

Note: Flexbox layout is most appropriate to the components of an application, and small-scale layouts, while the Grid layout is intended for larger scale layouts.

Parental properties

display

This defines a flex container; inline or block depending on the given value. It enables a flex context for all its direct children.

flex-direction

This establishes the main-axis, thus defining the direction flex items are placed in the flex container. Flexbox is (aside from optional wrapping) a single-direction layout concept. Think of flex items as primarily laying out either in horizontal rows or vertical columns.

row

default: left to right in ltr; right to left in rtl

row-reverse

right to left in ltr; left to right in rtl

column

same as row but top to bottom

column-reverse

same as row-reverse but bottom to top

row

row-reverse

column

column-reverse

flex-wrap

By default, flex items will all try to fit onto one line. You can change that and allow the items to wrap as needed with this property.

nowrap

default all flex items will be on one line

wrap

flex items will wrap onto multiple lines, from top to bottom.

wrap-reverse

flex items will wrap onto multiple lines from bottom to top.

nowrap

wrap

wrap-reverse

flex-flow

This is a shorthand flex-direction and flex-wrap properties, which together define the flex container's main and cross axes. Default is row nowrap.

nowrap

default all flex items will be on one line

wrap

flex items will wrap onto multiple lines, from top to bottom.

wrap-reverse

flex items will wrap onto multiple lines from bottom to top.

justify-content

This defines the alignment along the main axis. It helps distribute extra free space left over when either all the flex items on a line are inflexible, or are flexible but have reached their maximum size. It also exerts some control over the alignment of items when they overflow the line.

flex-start

default items are packed toward the start line

flex-end

items are packed toward to end line

center

items are centered along the line

space-between

items are evenly distributed in the line; first item is on the start line, last item on the end line

space-around

items are evenly distributed in the line with equal space around them. Note that visually the spaces aren't equal, since all the items have equal space on both sides. The first item will have one unit of space against the container edge, but two units of space between the next item because that next item has its own spacing that applies.

space-evenly

items are distributed so that the spacing between any two items (and the space to the edges) is equal.

flex-start

flex-end

center

space-between

space-around

space-evenly

align-items

This defines the default behaviour for how flex items are laid out along the cross axis on the current line. Think of it as the justify-content version for the cross-axis (perpendicular to the main-axis).

cross-start margin edge of the items is placed on the cross-start line

flex-end

items are packed toward to end line

center

items are centered along the line

baseline

items are aligned such as their baselines align

stretch

flex-start

flex-end

center

baseline

align-content

This aligns a flex container's lines within when there is extra space in the cross-axis, similar to how justify-content aligns individual items within the main-axis.

Note: this property has no effect when there is only one line of flex items.

stretch

default lines stretch to take up the remaining space

flex-start

lines packed to the start of the container

flex-end

lines packed to the end of the container

center

lines packed to the center of the container

space-between

lines evenly distributed; the first line is at the start of the container while the last one is at the end

space-around

lines evenly distributed with equal space around each line

stretch

flex-start

flex-end

center

space-between

space-around

Children properties

order

By default, flex items are laid out in the source order. However, the order property controls the order in which they appear in the flex container.

order

flex-grow

This defines the ability for a flex item to grow if necessary. It accepts a unitless value that serves as a proportion. It dictates what amount of the available space inside the flex container the item should take up.

If all items have flex-grow set to 1, the remaining space in the container will be distributed equally to all children. If one of the children has a value of 2, the remaining space would take up twice as much space as the others (or it will try to, at least).

flex-grow

flex-shrink

This defines the ability for a flex item to shrink if necessary.

flex-basis

This defines the default size of an element before the remaining space is distributed. It can be a length (e.g. 20%, 5rem, etc.) or a keyword. The auto keyword means "look at my width or height property" (which was temporarily done by the main-size keyword until deprecated). The content keyword means "size it based on the item's content" - this keyword isn't well supported yet, so it's hard to test and harder to know what its brethren max-content, min-content, and fit-content do.

If set to 0, the extra space around content isn't factored in. If set to auto, the extra space is distributed based on its flex-grow value. See this graphic.

flex

This is the shorthand for flex-grow, flex-shrink and flex-basis combined. The second and third parameters (flex-shrink and flex-basis) are optional. Default is 0 1 auto.

align-self

This allows the default alignment (or the one specified by align-items) to be overridden for individual flex items.

Please see the align-items explanation to understand the available values.

auto

flex-start

flex-end

baseline

stretch

svd.im — playground

Svd.im is the online playground of Sil van Diepen. You can find here small little projects and test Sil has been making. Nothing of this is ready, tested, done or anything. It's just for testing and fun. Feel free to check it out.